This is a picture of a speaker that uses a variable resistor in the sound knob to control the volume of the sound it produces. The resistance on the electrons flowing through the speaker changes as the knob is turned. When the knob is turned, a strip of metal or other conducting substance is moved, forcing the electrons to travel a longer path than before. According to the resistance equation, extending the path also increases resistance. When resistance is increased, less electrons reach their destination per second and less sound is produced.